Method of forming a laminate and the product thereof a laminate including a sealing agent and a bonding agent

ABSTRACT

Method for forming a laminate and a product formed therefrom. A thin layer of oil is applied to a facing surface of at least one of a plurality of adjacent sheets and a wax is applied along the longitudinal edges of a facing surface of at least one of the sheets. The sheets are combined into a laminate by being passed between a pair of rollers which apply sufficient pressure to remove excess oil from between the facing surfaces and to spread the wax thereby forming a continuous seal along the longitudinal edges of the laminate. Air between the facing surfaces is displaced by the oil and the wax forms the seal to prevent reentry of the air and seepage of the oil along the longitudinal edges of the laminate. The laminate is tightly held together to permit handling or fabrication without delamination.

This is a divisional of copending application Ser. No. 07/402310 filedon Oct. 5, 1989, now U.S. Pat. No. 5,018,267.

BACKGROUND OF THE INVENTION

This invention relates to a method of forming an improved laminate and alaminated core formed therefrom. More particularly, the inventionrelates to applying a liquid bonding agent and a sealing agent to thefacing surfaces of sheets and applying sufficient pressure to the sheetsto remove excess liquid bonding agent to displace air from between thefacing surfaces of the sheets while spreading the sealing agent toprevent reentry of the air and to prevent seepage of the liquid bondingagent along the edges of the sheets.

There are several applications such as electric power transformers,motors, electronics and catalytic converters employing thin gaugesheets. Thin gauge electrical steel sheets or amorphous metal sheets forelectrical applications reduce magnetically induced eddy currents byreducing the crosssectional area through which those currents may flow.Grain oriented steel sheets have a thickness less than 0.5 mm, typicallyin the range of 0.18 to 0.35 mm. Amorphous metal sheets typically have athickness of about 0.02 to 0.05 mm.

It is well known the above type electrical devices are more efficientwhen the thickness of the sheet is decreased with the lower limit forthe sheet thicknesses determined by manufacturing considerations.However, reducing the sheet thickness has undesirable effects onhandling and fabrication productivity. Handling tissue-like thin sheetsis a problem because the sheets are fragile and prone to damage duringhandling. The very thinness of the sheets reduces the productivityduring processing and fabrication, making the product more laborintensive to utilize.

The prior art discloses adhesives, varnishes, oxides or mixtures thereofwhich may be applied to the surfaces of sheets so that several of thesheets can be bonded (or laminated) together for simultaneousprocessing. Processing such a laminate greatly increases productivityand diminishes handling problems since the laminate is thicker and morerigid than a single sheet.

Nevertheless, there are several disadvantages when using adhesives,varnishes or oxides to bond sheets which are discussed at length in U.S.Pat. application Ser. No. 07/043,077, filed Apr. 27, 1987, having a newU.S. Pat. No. 4,882,834 common assignee and incorporated herein byreference. For example, to develop a good bond between sheets requiresthe bonding agent to be applied as a relatively thick layer creatingspace between adjacent sheets. This is undesirable for bonded laminatesused in electrical applications which are wound or stacked because theincreased spacing between the sheets decreases the space factor. Even athinly applied adhesive is undesirable because it tends to shrink whencured. Such a shrinkage, particularly for thin metal sheets, may strainor induce stress into the sheets. A further disadvantage when usingchemical bonding is that an elevated temperature may be required to curethe bonding agent. Such an elevated temperature may diminish the effectsof domain refinement treatments for electrical steel sheets. Anotherdisadvantage when using chemical bonding is that the sheets becomerigidly connected. Winding a rigidly formed electrical steel laminateinto a coil may induce stress thereby increasing core losses of thelaminate. A further disadvantage with chemical or ceramic bonding isthat the bonding layers tend to be brittle. Cutting, punching orcorrugating may fracture a brittle bonded layer causing the sheets todelaminate.

My pending patent application Ser. No. 07/043,077, now issued as U.S.Pat. No. 4,882,834, discloses a laminate can be formed that will resistseparation indefinitely by applying a liquid of an appropriate viscosityto the facing surfaces of sheets and applying sufficient pressure to thesheets to remove excess liquid and to displace air from between thefacing surfaces of the sheets. The liquid remaining between the facingsurfaces forms a seal preventing reentry of the air which enables thelaminate to resist separation during subsequent processing andfabrication. The laminate formed has no increase in the space betweenits sheets and no induced stress in its sheets. Unfortunately, some ofthe liquid remaining between the sheets seeps out from between thesheets along the sheet edges. Such seepage may cause a number ofphysical problems during subsequent processing of a laminate whenpunching to form stacked laminates. In the case where transformer oilwas used as the bonding liquid to form laminated electrical steelsheets, oil buildup on a punch press caused the laminate to slip in thedrive system, making it difficult to obtain precisely mitred cuts suchas are needed to build a transformer core from electrical steel sheets.Seepage also may result in the bonding liquid transferring onto theexterior surfaces of the laminated sheets so that stacked cut laminatedsheets become stuck together making it difficult to align properly in acore stack. Delamination may even occur when handling the laminatedsheets or punchings.

Accordingly, there remains a need for an improved technique for forminga laminate using a liquid bonding agent wherein seepage of the liquidbonding agent from between the facing surfaces of the formed laminate isminimized or prevented.

BRIEF SUMMARY OF THE INVENTION

This invention relates to a method of forming an improved laminate and alaminated core formed therefrom. A liquid bonding agent and a sealingagent are applied to a facing surface of at least one of a plurality ofsheets. Pressure is applied to the sheets to remove excess liquidbonding agent and to displace air from between the facing surfaces ofthe sheets and to spread the sealing agent to form a continuous barrieralong each longitudinal edge of the formed laminate to minimize seepageof the liquid bonding agent along the longitudinal edges of thelaminate.

Principal objects of my invention are to form a laminate using a liquidbonding agent wherein the laminate resists separation, has no decreasein its space factor, and can be fabricated without delamination.

A feature of my invention is to form a laminate from two or more sheetsusing a liquid bonding agent and a sealing agent.

Another feature of my invention is to form a laminate using a liquidbonding agent by applying a sealing agent along longitudinal edges of atleast one facing surface of a plurality of sheets to form a continuousbarrier to prevent seepage of the liquid bonding agent along thelongitudinal edges of the formed laminate.

Another feature of my invention is to form a laminate using a liquidbonding agent by applying a sealing agent along longitudinal edges andat a position intermediate the longitudinal edges to at least one facingsurface of a plurality of sheets to form continuous barriers along thelongitudinal edges and at the intermediate position, slitting thelaminate along the intermediate position into narrower width laminates,whereby the sealing agent prevents seepage of the liquid bonding agentalong the longitudinal edges of the formed laminates.

Another feature of my invention is to form a laminate using a lowviscosity liquid bonding agent and a high viscosity sealing agent toprevent seepage of the bonding agent along longitudinal edges of theformed laminate.

Another feature of my invention is to form a laminate using a liquidbonding agent having a viscosity no greater than about 80 cP at 24° C.and a sealing agent having a viscosity no greater than about 2500 cP at24° C.

Another feature of my invention is to form a laminate by providing atleast two sheets each having a facing surface, applying a liquid bondingagent to one of the facing surfaces of the sheets, applying a sealingagent along the longitudinal edges of one of the facing surfaces,applying pressure to the sheets to remove excess liquid bonding agentfrom between the surfaces and forming a continuous barrier by spreadingthe sealing agent between the surfaces as the surfaces are brought intocontact with each other, whereby air between the surfaces is displacedby the liquid bonding agent and the sealing agent prevents reentry ofthe air and minimizes seepage of the liquid bonding agent along theedges of the formed laminate.

Another feature of my invention is to form a laminate from a pluralityof grain oriented steel sheets each having a facing surface and athickness less than about 0.5 mm, passing the sheets along a feedpath ata predetermined speed, applying a liquid bonding agent having aviscosity no greater than about 80 cP at 24° C. to one of the facingsurfaces, applying a sealing agent having a viscosity no greater thanthan 2500 cP at 24° C. along the longitudinal edges of one of the facingsurfaces, passing the sheets between a pair of rollers, applyingpressure to the sheets by the rollers to remove excess liquid bondingagent from between the surfaces and forming a continuous barrier by thesealing agent between the facing surfaces as the facing surfaces arebrought into contact with each other, whereby air between the surfacesis displaced by the liquid bonding agent and the sealing agent preventsreentry of the air and minimizes seepage of the liquid bonding agentalong the edges of the formed laminate.

Advantages of my invention include reduction in manufacturing costs of alaminate which can be slit, cut or punched with little or no seepage ofthe liquid bonding agent and production of fabricated cores using thelaminates whose sheets are free from strain and induced stress.

The above and other objects, features and advantages of my inventionwill become apparent upon consideration of the detailed description andappended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic showing two sheets moving along a feedpath beinglaminated together by a pair of sealing rollers and the laminate beingwound into a coil,

FIG. 2 is a cross-section view along line 2--2 of FIG. 1,

FIG. 3 shows an enlarged fragmentary cross-section view of laminatedsheets of my invention,

FIG. 4 shows an enlarged longitudinal section view of two sheets beingpressed together according to my invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, reference numeral 12 denotes a sheet being uncoiledfrom a coil 10 and fed at a predetermined speed along a feedpath 13while passing over a wax applicator 17. Another sheet 16 is fed at thesame speed from a coil 14 under an oiling roller 18. Sheet 16 is broughttogether with sheet 12 by a change of direction roller 20.

For my invention, it will be understood a sheet is meant to includecontinous strip, foil, ribbon and the like as well as strip cut intoindividual lengths. Preferably, the sheet will include cold reduced orcast steel and amorphous base metals having a thickness of less thanabout 0.5 mm. A more preferred sheet includes grain oriented steelhaving a glass insulative coating on both sides of the sheet with atotal thickness of the sheet and coating layers less than about 0.35 mm.U.S. Pat. No. 3,948,786--Evans, incorporated herein by reference,discloses grain oriented steel having Mg-PO₄ glass insulative coatings.

Wax applicator 17 can be any conventional mechanical device such as asprayer, a capillary-action applicator, a wiping-type roller, anextruder, and the like. For example, wax applicator 17 may include aheater 19, a feed tube 21, and a plurality of nozzles 23 for applying asealing agent 34 along each longitudinal edge of the facing surface ofsheet 12. Oiling roller 18 applies a thin coating of a liquid bondingagent to the facing surface of sheet 16. Sheets 12 and 16 pass between apair of sealing or consolidation rollers 22 and 24 which applysufficient pressure to sheets 12 and 16 so that the adjacent (facing)surfaces of sheets 12 and 16 are brought into intimate contact with eachother. Continuous films of liquid bonding agent and sealing agentsubstantially displace all air between the facing surfaces to form alaminate 26. Laminate 26 is wound around a mandrel 28 forming a coil 30.

The clearance between rollers 22 and 24 preferably should not be lessthan the combined thicknesses of sheets 12 and 16. For grain orientedsheets, rollers 22 and 24 must apply sufficient pressure to removeexcess liquid bonding agent to displace air and to spread the sealingagent to form a continuous barrier or seal along both longitudinal edgesof the formed laminate without inducing stress into sheets 12 and 16.

FIG. 1 illustrates how a sealing agent is applied by wax applicator 17to the bottom (facing) surface of sheet 12 and a liquid bonding agent isapplied by roller 18 to the top (facing) surface of sheet 16. Waxapplicator 17 also could be used to apply the sealing agent to the top(facing) surface of sheet 16 and roller 18 could be used to apply theliquid bonding agent to the bottom (facing) surface of sheet 12.Alternatively, the bonding agent and the sealing agent could be appliedto both of the facing surfaces of sheets 12 and 16. It will beunderstood the sealing agent can be applied to a facing surface of asheet in a number of patterns such as a continuous line, parallel lines,squares, cross-hatched lines, sinusoidal lines, an extruded bead, andthe like so long as a continuous barrier is formed along thelongitudinal edges when laminating the sheets. The liquid bonding agentcan be applied as a roller coating or sprayed as a fine mist. Dependingon the equipment available, the number of sheets simultaneously fedalong feedpath 13 and the type of material being laminated, it may beadvantageous to apply the liquid bonding agent and the sealing agent toa sheet during a previous processing operation. In any event, the liquidbonding agent and sealing agent are applied only to sheet surfaces whichare facing surfaces when the sheets are combined into a laminate.

FIG. 2 illustrates a cross-section of sheets 12 and 16 taken along line2--2 of FIG. 1 before sheets 12 and 16 are combined by rollers 22 and 24into laminate 26. Small beads of sealing agent 34 are placed along eachof the longitudinal edges 36 and 38 on facing surface 32 of sheet 12. Athin film 42 of the liquid bonding agent is placed on facing surface 40of sheet 16. If laminate 26 is to be slit into narrower widths,additional sealing agent would be applied longitudinally along facingsurface 32 at those positions where the laminate is to be slit. For anelectrical steel laminate that is to be slit and mitred into corepunchings at an angle of 45 degrees, the additional sealing agentapplied at those positions to be slit preferably would be in a patternsuch as square, cross-hatched, or sinusoidal to insure the sealing agentextends continuously along the longitudinal and transverse edges of theslit and cut laminates.

FIG. 3 illustrates an enlarged fragmentary cross-section view of aportion of laminate 26 formed from sheets 12 and 16 illustrated inFIG. 1. The planar surfaces of metallic sheets normally are notperfectly flat and are somewhat roughened. This means facing surface 32of sheet 12 will not be in continuous contact with an adjacent facingsurface 40 of sheet 16. Facing surfaces 32 and 40 engage each other atpoint contacts 44. As sheets 12 and 16 are brought into contact witheach other by rollers 22 and 24, void areas 46 representing non-contactpoints between surfaces 32 and 40 are filled with liquid bonding agent42. Sealing agent 34 is spread to form thin continuous barriers or damsalong the longitudinal edges of laminate 26. FIG. 3 illustrates a thinbarrier 34a formed by rollers 22 and 24 by spreading sealing agent 34along longitudinal edge 38. The separation between surfaces 32 and 40 atnon-contact points, i.e. void areas 46, will be less than about 0.005mm. Air is displaced as excess liquid bonding agent is squeezed frombetween surfaces 32 and 40. A continuous film of sealing agent 34aformed along longitudinal edges 36 and 38 between surfaces 32 and 40 ofsheets 12 and 16 prevents reentry of the air and prevents seepage ofliquid bonding agent 42 from between facing surfaces 32 and 40 along thelongitudinal edges of laminate 26. Accordingly, sheets 12 and 16 aretenaciously held together. Without barriers 34a along the longitudinaledges, liquid bonding agent 42 could seep out from between the sheetfacing surfaces as illustrated by seepage 42a.

FIG. 2 illustrates beads 34 of sealing agent being applied alonglongitudinal edges 36 and 38 of sheets 12 and 16. If laminate 26illustrated in FIG. 3 is slit longitudinally into two or more narrowerwidth laminates, liquid bonding agent 42 could seep from between facingsurfaces 32,40 along the newly cut longitudinal edges of the narrowerlaminates. In this situation, it is desirable to apply additionalsealing agent 34 along the facing surface of the sheet at thosepositions corresponding to where the sheet would be slit so that bothlongitudinal edges of each laminate include a continuous sealing barrier34a. For a laminate to be slit into two laminates of equal width,sealing agent 34 would be applied to the facing surface approximatelymidway between opposing edges 36,38.

Not being bound by theory, it is believed the laminate is tightly heldtogether by a pressure differential existing between voids 46 filledwith the liquid bonding agent and/or sealing agent and the ambientatmospheric pressure surrounding laminate 26. In other words, sheets 12and 16 resist delamination since the interlaminar pressure uponseparation would decrease below ambient atmospheric pressure pushingagainst the outside surfaces of laminate 26 as illustrated by arrows 48in FIG. 4. Facing surfaces 32 and 40 of sheets 12 and 16 respectivelyinclude a bead of sealing agent 34 and a thin layer of liquid bondingagent 42. Sheets 12 and 16 are being fed from left to right through thebite of rollers 22 and 24. As rollers 22 and 24 bring surfaces 32 and 40into intimate contact with each other, a meniscus 50 is formed anddisplaces air 52 as sealing agent 34 and excess liquid bonding agent 42are displaced from between facing surfaces 32 and 40.

The liquid bonding agent can be any low viscosity liquid preferablyhaving a viscosity no greater than about 80 cP at 24° C. when applied tothe sheets. Using a bonding agent having a higher viscosity makes itdifficult to obtain a good space factor and to avoid shifting of thelaminated sheets. Acceptable bonding agents include water, alcohol, oiland the like. For higher viscosity bonding agents, it may be desirableto heat the bonding agent to a temperature above ambient for applicationto the sheet. For cut electrical steel sheets, the bonding agent isformed into a continuous film to provide for continuous interlaminarinsulation to preserve magnetic quality. A natural or synthetictransformer oil is preferred for this purpose. The importantconsiderations are that the bonding agent adequately wets the surfacesof the sheets, is compatible with the environment in which the laminatewill be used, and has the necessary viscosity.

For a sealing agent, a relatively high viscosity liquid or a solid suchas wax can be used having a viscosity preferably greater than about 250cP at 24° C. Waxes having a viscosity greater than about 2500 cP at 24°C. are difficult to extrude. The added force necessary to extrude thickresin-like waxes could produce microplastic strain to the sheets whichwould harm the core loss of electrical steel. A sealing agent which issolid at ambient temperature, such as hard beeswax, would induce coilset and harm the stress condition of electrical steel. As in the case ofthe liquid bonding agent, it may be desirable to heat higher viscositysealing agents to a temperature above ambient for application to sheets.The important considerations for the sealing agent are the same as thatfor the liquid bonding agent and additionally to have sufficientviscosity to retard or prevent seepage of the liquid bonding agentthrough the continuous barriers formed along the longitudinal edges ofthe laminate.

Viscosity is a measurement of a liquid's resistance to flow due to theattraction between molecules. The greater the attractive force, theslower the liquid is to flow. The viscosity of the liquid bonding agentand the sealing agent used is important because it effects the flow rateof meniscus 50 between facing surfaces 32 and 40 when joined together byrollers 22 and 24 as illustrated in FIG. 4.

As disclosed in pending patent application Ser. No. 07/043,077, I havedetermined experimentally that a variety of low viscosity liquidsperform well as a bonding agent. Cores used as transformers in electricpower transmission frequently are permanently immersed in and cooled bya transformer oil. Using this oil as the bonding liquid is particularlyadvantageous in that it is compatible with the transformer oil. For someapplications, the formed core may receive a final heat treatment beforeits end use. For those heat treated cores where carbon in a hydrocarbonbased liquid bonding agent could contaminate the sheet base metal, i.e.grain oriented steel, a synthetic non-carbonaceous oil could be used asthe bonding agent.

EXAMPLE 1

By way of example, conventional grain oriented electrical steel sheets7.65 cm wide, 30.5 cm long and 0.18 mm thick were coated with a 5-6gm/m² insulative coating applied over a mill glass coating. In tests1-3, only a liquid bonding agent was applied to the sheets. A siliconetype transformer oil having a nominal viscosity of 40 cP at 24° C. wasapplied by brushing oil onto one facing surface of each pair of thesteel sheets. Two sheets were laminated by passing the sheets through apair of 76 mm diameter neoprene rollers and applying sufficient pressureto remove excess transformer oil and to displace air from between thefacing surfaces. In tests 4-6, only a sealing agent was used. An organicwax having a viscosity of 500 cP at 24° C. was applied by contact wipingonto one facing sheet surface as a series of parallel lines each havinga width of about 10 mm and spaced at about 25 mm intervals along thelongitudinal (rolling) direction of the sheets. The wax sealing agentwas spread into a thin film between the facing surfaces of the sheets byapplying sufficient pressure to the exterior surfaces of the sheets. Allthe tests were evaluated immediately after laminating and aftersubjected to metal cutting. Tests 1-3 resulted in good quality laminatesand preserved the intrinsic magnetic quality of the grain orientedelectrical steel. Average core loss at 15 kG and 17 kG was increased by0.8% and 0.9% respectively. However, seepage of the transformer oil frombetween the sheets along the edges was evident during consolidation ofthe sheets and during shearing of the laminates. As was expected fortests 4-6, seepage did not occur since only a high viscosity sealingagent was used. However, the laminates produced were of poor qualitywhich experienced considerable deterioration in their magnetic qualitywhen sheared. Average core loss at 15 kG and 17 kG increased 5.1% and5.2% respectively. Tests 4-6 demonstrate that the use of a sealing agentalone without a liquid bonding agent to form a continuous film betweenthe sheet facing surfaces will not prevent deterioration of magneticquality. Metal-to-metal contact, i.e. interlaminar "shorting", occurswhen continuous interlaminar insulation is lacking and producescirculating or eddy currents during AC magnetization. This shorting isthe result of loss of the insulative coating from the sheet surfaces ifthe formed laminate is cut when making cores. When a continuous film ofthe liquid bonding agent is present, the insulative coating still flakesoff when cutting the metal sheets but the bonding agent apparently holdsthe powdered insulative coating at the point of cutting keeping thesheets from coming into contact with each other.

EXAMPLE 2

High permeability oriented electrical steel sheets 7.65 cm wide, 30.5 cmlong and 0.23 mm thick were coated with a 9-10 gm/m² insulative coatingapplied over a mill glass coating. In tests 7-10, the same liquidbonding agent was applied in a similar manner to that for tests 1-3above. The same sealing agent and a similar method of application tothat for tests 4-6 was used for tests 11-14 except the sealing agent wasapplied in a series of parallel bands with each band having a width ofabout 10 mm and spaced at about 30 mm intervals. All the tests againwere evaluated immediately after laminating and after subjected to metalcutting. The results for the laminates produced from tests 7-14 weresubstantially the same as reported above for tests 1-6. Magnetic qualityfor laminates made from tests 7-10 using only a liquid bonding agent wasgood but seepage of the bonding agent occurred during consolidation ofthe sheets and after shearing of the laminates. Average core loss at 15kG and 17 kG increased -0.3% and 0.8% respectively. The laminatesproduced from tests 11-14 were of poor quality and the average core lossat 15 kG and 17 kG increased 2.4% and 4.3% respectively.

EXAMPLE 3

Additional laminates were prepared according to the invention fromsheets identical to those for Example 2. Sheets for tests 15-17 had thesame liquid bonding agent and manner of application as described fortests 1-3 in Example 1. After applying the liquid bonding agent to thesheets, the sealing agent described for tests 4-6 in Example 1 wasapplied also to tests 15-17 in the form of a 10 mm wide bead along thelongitudinal and transverse edges of the sheets. The sheets wereconsolidated into laminates in the same manner as that described fortests 4-6 in Example 1. No seepage of the bonding agent along any of theedges of the laminates occurred after consolidation of the sheets orafter shearing of the laminates. The magnetic quality of the laminateswas excellent both before and after shearing. The average core loss for15 kG and 17 kG was well within the range of the test results reportedabove when only liquid bonding agent was used for tests 1-3 for Example1 or tests 7-10 for Example 2. During consolidation of the sheets, itwas demonstrated the sealing agent was spread into a thin continuousfilm along the edges of the formed laminates which retained the liquidbonding agent between the facing surfaces of the sheets forming thelaminates.

Results of the trials discussed above are summarized in Table 1.

                  TABLE 1                                                         ______________________________________                                                                     Seepage                                          Test No. Laminate Quality After Shearing                                                                   After Shearing?                                  ______________________________________                                        1        good                yes                                              2        good                yes                                              3        good                yes                                              4        poor                no                                               5        poor                no                                               6        poor                no                                               7        good                yes                                              8        good                yes                                              9        good                yes                                              10       good                yes                                              11       poor                no                                               12       poor                no                                               13       poor                no                                               14       poor                no                                               15 (invention)                                                                         good                no                                               16 (invention)                                                                         good                no                                               17 (invention)                                                                         good                no                                               ______________________________________                                    

While only one embodiment of my invention has been described, it will beunderstood various modifications may be made to it without departingfrom the spirit and scope of it. For example, various liquid bondingagents and sealing agents may be used so long as they are compatiblewith the environment within which the laminate is to be used and havethe necessary viscosity to form a seal when formed into very thinlayers. Two or more sheets may be laminated simultaneously using variousmeans to apply the liquid bonding agent and sealing agent to the facingsurfaces of at least one of the sheets. One or both surfaces of thesheets may have previously applied coating such as metallic or glassinsulative coatings. The laminate may be wound into a core, formed intoa stacked core of cut laminates or otherwise fabricated. Therefore, thelimits of my invention should be determined from the appended claims.

I claim:
 1. A laminate, comprising:at least two sheets each having a facing surface, said surfaces in contact with each other, a sealing agent along the longitudinal edges on said surfaces and a liquid bonding agent between said sealing agent on said surfaces, said sealing agent having a viscosity of no greater than 2500 cP at 24° C. and said liquid bonding agent having a viscosity no greater than about 80 cP at 24° C. air between said surfaces being displaced by said liquid bonding agent and said sealing agent, said sealing agent forming a continuous barrier to prevent reentry of said air and minimizing seepage of said liquid bonding agent along said edges, whereby said laminate can be handled without delamination.
 2. The laminate as set forth in claim 1 wherein said liquid bonding agent is an oil and said sealing agent is a wax.
 3. The laminate as set forth in claim 1 wherein said surfaces include a glass insulating coating impervious to said liquid bonding agent and said sealing agent, each of said sheets being grain oriented steel having a thickness less than about 0.5 mm.
 4. A metallic core, comprising:at least one laminate, said laminate including at least two sheets each having a facing surface, said sheets having a thickness of less than about 0.5 mm, said surfaces in contact with each other, a sealing agent along the longitudinal edges on said surfaces and a liquid bonding agent between said sealing agent on said surfaces, said sealing agent having a viscosity of no greater than 2500 cP at 24° C. and said liquid bonding agent having a viscosity of no greater than about 80 cP at 24° C. air between said surfaces being displaced by said liquid bonding agent and said sealing agent, said sealing agent forming a continuous barrier to prevent reentry of said air and minimizing seepage of said liquid bonding agent along said edges, whereby said core can be handled without delamination of said laminate.
 5. The core as set forth in claim 4 wherein said core is a wound electrical transformer. 